An apparatus for carrying out stampings and perforations on printed or unprinted papers on rotary printing presses is known from U.S. Pat. No. 3,554,070. In this known device, the tools consist of angled strips with one long and one short leg. The short leg runs at right angles to the long leg and is designed as a cutting edge. Depending on the effect desired, the cutting edge is designed to be either continuous or interrupted. For perforating, for example, it is saw-tooth-like in form. The strips are provided with glue on the under surface of the long leg and are glued into position directly on the impression cylinder of known rotary printing presses. This impression cylinder is in contact, in the known way, with the blanket cylinder, which in turn is in contact with the plate cylinder. After the strips are arranged in the desired position on the impression cylinder, the paper to be processed is conducted between the impression and the blanket cylinders, and the cutting edges of the strips perforate the paper at the desired places. At the same time, a printed image may be transferred to the paper from the plate cylinder via the blanket stretched on the blanket cylinder.
In practice it has been found that a simultaneous printing and perforation or stamping of the paper is only possible at the cost of considerable lowering of quality of the printed product. The cutting edges of the strip, striking through the paper, damage the rubber blanket on the blanket cylinder and leave cuts in the rubber blanket surface. Thus, the rubber blanket can no longer be used for further printing runs and must be replaced. Moreover, the gluing of the strip-form tools to the impression cylinder is also time-consuming and costly. In the case of perfecting presses with roughened impression cylinders, the tools cannot be glued on, since they will not hold to the surface of the impression cylinder or will smear the freshly printed sheet. A further disadvantage found is that the leg of the strip bearing the cutting edge can only have a maximum height which corresponds to the distance between the surface of the impression cylinder and the surface of the rubber blanket on the blanket cylinder. Since in this space the support leg of the tool must also fit, the cutting edges do not extend over the whole height of the short leg, and the paper may either not be completely cut through, or raised places as well as tool marks are formed on the paper. As a result of the former, the paper parts cannot be perfectly separated from each other, and as a result of the latter, no high stacks of finished sheets of paper can be formed.
According to Swiss Pat. No. 587,107, the idea is known, in rotary stamping or die-cutting presses, of placing the cutting strip on a sheet by means of a binder, and then mounting this sheet on the stamping cylinder. The use of this process in rotary printing presses involves additional disadvantages, since the sheet mounted on the impression cylinder reduces the space between the impression cylinder and blanket cylinder, necessary to allow the paper to run through. In some types of machine, the placement of a sheet provided with strips on the impression cylinder is only possible with very great difficulty.
The present invention attacks the problem of avoiding the disadvantages of the known technology and providing a solution by which perforation, stamping or creasing of paper or cardboard on rotary printing presses can be carried out perfectly, without parts of the press or of the printing equipment being damaged. The solution should also make possible a shortened downtime of the rotary printing press and permit high work speeds.
The problem is solved by the invention, as to processing, by the fact that in a first work step, the rubber blanket is removed from the blanket cylinder and, in place of the blanket, a base sheet with pre-mounted strips is placed on the blanket cylinder. The base sheet is prepared outside the machine before stopping the rotary printing press, with the strips arranged in the desired position thereon. By changing the distance between the blanket cylinder and impression cylinder, the desired depth of tool engagement and the desired working pressure are set, at which time the paper or cardboard to be processed can be conducted between the blanket cylinder and the impression cylinder. In a further embodiment of the process, before the processing of the paper or cardboard, either simultaneously with or after the placing of the base sheet on the blanket cylinder, a second sheet is placed on the impression cylinder.
The apparatus for carrying out this process on rotary printing presses is distinguished by the fact that on the blanket cylinder, instead of the rubber blanket, there is located a base sheet on which are fastened strips which have a desired perforating, stamping or creasing profile, and that on the impression cylinder there is arranged a flat sheet. The strips have, advantageously, a T-shaped cross section, and the middle part is equipped with the desired profiling and cutting edge. In a further embodiment of the invention, the middle part of the strip is at least 1 mm high.
The advantages attained through the invention are mainly to be seen in the fact that, in the perforating, stamping or creasing of the paper or cardboard, neither the rubber blanket nor the sheet of paper or cardboard are damaged by the strips. By the removal of the rubber blanket, moreover, additional space is gained between the blanket cylinder and the impression cylinder, by which greater thicknesses of paper can be processed. The middle part of the strip, bearing the cutting edge, can also be designed to be high enough so that the cutting edge penetrates completely through the paper and no wrinkled places result. Also, tool marks on the paper can be eliminated. Moreover, there is an important shortening of the downtime of the machine, since the sheet with the strips can be prepared independently of the machine and mounted accurately and fastened by means already present on the blanket cylinder for the fastening of the blanket. The downtime of the machine can be shortened by at least 50% as compared with the process of gluing strips onto the impression cylinder. A further advantage is that the sheets can be used several times, since after the end of the finishing process, they can be removed from the blanket cylinder and stored. After removal of the base sheet with the strips, the blanket cloth can be remounted and the printing process continued. For similar perforation, stamping or creasing work, the prepared base sheet can be taken from storage and mounted instead of the blanket, on the blanket cylinder. This means that the strips can be used several times. Dull strips can also be sharpened to increase their life. This process according to the invention and the corresponding apparatus make it possible, even for print shops having only one rotary printing press and no stamping machine, to carry out perfect perforation, stamping and creasing jobs.